U.S. patent number 5,963,138 [Application Number 09/019,182] was granted by the patent office on 1999-10-05 for apparatus and method for self adjusting downlink signal communication.
This patent grant is currently assigned to Baker Hughes Incorporated. Invention is credited to Hartmut H. Gruenhagen.
United States Patent |
5,963,138 |
Gruenhagen |
October 5, 1999 |
Apparatus and method for self adjusting downlink signal
communication
Abstract
An apparatus for sending signals downhole during drilling
operations uses a main pump to pump mud from a mud pit at a
substantially constant flow rate. The bulk of the pumped mud goes
downhole to maintain adequate circulation for the drill bit. A
bypass pipe is provided with a shut-off valve that is controlled by
an electronic controller. By pulsing the opening and closing of the
shut-off valve, the volumetric flow downhole is pulsed. The pulse
amplitude and duration can be controlled. These pulses in the flow
rate are detected by a suitable downhole device such as a flow rate
measurement device, a pressure detector or a turbine. The initial
"wake-up" pulse is made long enough so that the detection device
downhole is always able to detect it. Subsequent to this wake-up
pulse, adjustments are made to the pulse duration, in steps of
about 2 seconds, for the smallest pulse period that is detectable
downhole. In addition, the amplitude of the pulses is also
controlled by regulating the maximum flow through the shut-off
valve. The pulses are modulated by a binary sequence of numbers
corresponding to the data to be transmitted.
Inventors: |
Gruenhagen; Hartmut H.
(Hermannsburg, DE) |
Assignee: |
Baker Hughes Incorporated
(Houston, TX)
|
Family
ID: |
21791859 |
Appl.
No.: |
09/019,182 |
Filed: |
February 5, 1998 |
Current U.S.
Class: |
340/679;
340/853.3; 367/83; 175/40; 340/853.1; 340/853.6; 367/43 |
Current CPC
Class: |
E21B
41/00 (20130101); E21B 21/08 (20130101); E21B
47/18 (20130101); E21B 47/24 (20200501) |
Current International
Class: |
E21B
47/12 (20060101); E21B 47/18 (20060101); E21B
21/00 (20060101); E21B 21/08 (20060101); E21B
41/00 (20060101); G08B 021/00 () |
Field of
Search: |
;340/679,853.3,853.5,606,609,853.6,853.1,384.3,855.5
;367/83,43,84,85 ;73/151 ;175/128,40 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lefkowitz; Edward
Assistant Examiner: Woods; Davetta
Attorney, Agent or Firm: Madan & Morris, P.C.
Claims
We claim:
1. An apparatus for transmitting data during drilling operations
between a surface location and a downhole location in a borehole
comprising:
(a) a pump at the surface for pumping mud from a source
thereof;
(b) a conduit for transporting the mud to the borehole;
(c) a by-pass coupled to the conduit for selectively diverting the
flow of mud in the conduit;
(d) a flow control device associated with the by-pass;
(e) a controller operatively connected to the flow control device
to control the flow through the flow control device and cause a
pulsed variation in the pressure of the mud in the conduit
indicative of the data to be transmitted; and
(f) a downhole detection device adapted to detect said pulsed
variation in the pressure of the mud.
2. The apparatus of claim 1 wherein the flow control device is a
valve having an open position and a closed position.
3. The apparatus of claim 2 further comprising a throttle
associated with the by-pass, said throttle adapted to adjust the
maximum rate of flow through the by-pass.
4. The apparatus of claim 2 wherein the valve is a disk valve with
a fixed slot and a rotatable slot, the rotatable slot adapted to be
moved in response to a signal from the controller to adjust a
maximum rate of flow in the valve.
5. The apparatus of claim 1 wherein the controller is a
computer.
6. The apparatus of claim 1 wherein the pulsed variation in the
pressure of the mud further comprises a "wake-up" pulse having a
length followed by a sequence of square wave pulses having an
amplitude and a period.
7. The apparatus of claim 6 wherein the downhole detection device
is further adapted to send a response signal indicative of
detection of a square wave pulse.
8. The apparatus of claim 7 wherein controller changes said
amplitude of the square wave pulses after a predetermined time
interval upon failure to receive a response signal at the surface
location.
9. The apparatus of claim 7 wherein the controller changes said
amplitude of the square wave pulse and said period of the square
wave after a predetermined time interval upon failure to receive a
response signal at the surface location.
10. The apparatus of claim 1 wherein the downhole detection devices
comprises a flow rate measurement device.
11. The apparatus of claim 1 wherein the downhole detection devices
comprises a pressure detector.
12. The apparatus of claim 1 wherein the downhole detection device
comprises a turbine/generator combination.
13. A method for transmitting data during drilling operations
between the surface and a downhole location in a borehole
comprising:
(a) pumping mud from a source thereof through a conduit into a
drill string disposed in the borehole;
(b) using a controller to divert part of the mud into a by-pass
coupled to the conduit, thereby changing a rate of flow of the mud
in the conduit and generating mud pulses indicative of the data to
be transmitted, said mud pulses having a predetermined rate and an
amplitude; and
(c) detecting the mud pulses downhole and transmitting to the
controller a response signal indicating detection of said
pulses.
14. The method of claim 13 further comprising using the controller
to change the characteristics of the mud pulses upon failure to
receive a response signal within a predetermined interval by
changing at least one of (i) the amplitude of the mud pulses, and
(ii) the predetermined rate of the mud pulses.
15. The method of claim 13 further comprising using the controller
to generate a "wake up" pulse, said "wake-up" pulse having a
period, preceding the mud pulses having an amplitude and a
predetermined rate.
16. The method of claim 13 further comprising using a flow control
device in the by-pass, said flow control device being operated by
the controller.
17. The apparatus of claim 1 wherein the pump at the surface pumps
mud at a substantially constant flow rate.
18. The method of claim 13 wherein the step of pumping mud further
comprises pumping mud at a substantially constant flow rate.
Description
FIELD OF THE INVENTION
The invention relates to the control of downhole drilling equipment
by a mud pulse telemetry system, and particularly to an automatic
adjustment of the pulse amplitude and duration to account for the
attenuation of signals at increased depth.
BACKGROUND OF THE INVENTION
Well bores or boreholes are drilled using a drilling assembly (also
referred to as the "bottom hole assembly" or "BHA") carrying a
drillbit at its bottom hole end. The BHA includes a variety of
sensors to gather information about the wellbore and subsurface
formations along with associated processing circuits and
microprocessors. Data and signals are transmitted from the surface
to control the operation of devices in the BHA. Such devices
include motors, hydraulic devices, etc. A number of signal
transmission methods have been used to send signals from the
surface to a receiver in the BHA. In one such method, an acoustic
signal carried by the mud or by the drillstring is used.
Electromagnetic signals carried by the drillstring have also been
used to transmit information downhole. However, these methods are
difficult to use in measurement-while-drilling ("MWD") operations
because of the necessity of maintaining an adequate mud flow for
drilling operations and of the noise associated with the mud flow
and with the rotating drillstring. A common method of communicating
the signals downhole is via drilling fluid pressure pulses ("mud
pulses") generated by altering the rate of flow of the drilling mud
used in drilling operations.
This is fraught with problems because of the wear and tear on the
mud pumps from constant starting and stopping. A major accompanying
problem is that the mud pulses attenuate and disperse as they
propagate through the drilling mud. This dispersion is unavoidable
and is caused by various mechanisms, including viscous dissipation
in the drilling mud as well as frictional energy loss at the
borehole walls. This problem is exacerbated with increasing depth
of the wellbore. When a square wave is transmitted through a
dispersive medium, the received signal is no longer a square wave;
instead of a sharp change in amplitude corresponding to the leading
and trailing edges of the square wave, the received signal shows a
gradual change in amplitude. In addition, the received signal is
attenuated compared to the transmitted signal.
Because of the dispersion and attenuation of the signal, detection
of the onset of the pulses and the determination of their duration
can be difficult. Without proper decoding of the pulses, control of
the downhole equipment is lost. As noted above, the problem gets
worse as drilling depth increases due to increased attenuation and
dispersion. The ability to detect pulses determines the bandwidth
of the mud pulse telemetry link. Prior art techniques have relied
on an ad hoc method of dealing with the problem: the pulse duration
is increased by predetermined increments as the drilling depth
increases. As an example, a pulse duration of 8 seconds is used at
shallow depths, of 12 seconds at intermediate depths and of 16
seconds at large depths. This is an inefficient procedure for as it
does not allow for maximum data transmission based on the available
bandwidth of the data channel. Furthermore, the limited choice of
available pulse duration means that if the predetermined discrete
values are inadequate, the entire drillstring has to be brought to
the surface to adjust the downhole tool for another data rate.
It is desirable to have a method and an apparatus for adjusting the
pulse telemetry that automatically adjusts for the attenuation of
the signal by adjusting the data rate. The method should preferably
make use of the full available bandwidth for signal transmission.
It should also not require retrieval of the downhole equipment to
modify the data transmission rate. The present invention provides a
downhole telemetry system that automatically adjusts the data rate
as a function of the deterioration of the transmitted signal during
drilling of the wellbore.
SUMMARY OF THE INVENTION
The present invention is a self adjusting communication link
incorporating a mud-pulse telemetry system for controlling downhole
devices. A main pump operating at a substantially constant flow
rate pumps mud from a source thereof, such as a mud pit. The bulk
of the pumped mud goes downhole to maintain adequate circulation
through the wellbore. A bypass conduit or path is provided with a
fluid flow control device that is controlled by a control unit or
circuit. The amplitude and duration of the mud pulses are
controlled by pulsing the fluid control device. These mud pulses
are detected downhole by a suitable device, such as a flow rate
measurement device, a pressure detector or a turbine. The initial
or "wake-up" pulse is made long enough so that the detection device
downhole is always able to detect the wake up pulse. Subsequent to
the wake-up pulse, the duration of the data pulses is adjusted, as
the drilling progresses, near the smallest duration that is
detectable downhole. In the preferred embodiment, the pulse
durations are incremented in one or two second increments
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a drilling rig using the
present invention.
FIG. 2 illustrates the pulse-like pattern of a variation in
volumetric flow during the transmission of signals.
FIGS. 3a-3e illustrate the various types of pulse shapes used to
transmit signals downhole according to the present invention.
FIG. 4 illustrates the modulation of a square wave by a data
sequence.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is best understood by reference to the FIGS.
1-3. FIG. 1 is a schematic illustration of a drilling rig 1 that
has a swivel head 3 to which is attached the drill string 2. At the
bottom of the drill string 2 is a drilling tool 4. The drilling
tool 4 is conveyed in the borehole 5 and includes a housing 6.
Attached to the housing are stabilizers 7, 8 for stabilizers for
reducing vibrations and a non-rotating sleeve 9 with ribs 10 that
can be extended and retracted in a controlled fashion. The ribs are
used to control the direction of drilling of the tool. The
non-rotating sleeve 9 maintains a substantially fixed orientation
in the borehole, independent of the rotation of the drill string 2.
The drilling tool 4, together with the drill head 12 can be caused
to rotate by using the drill string 2.
FIG. 1 also shows a mud pit 13 in which there is a supply of
drilling mud 14. A mud pump 15 has an inlet pipe 15a dipping into
the mud and a main pipe 16 connected to the swivel head 3. A return
pipe 17 connected to the wellhead equipment 18 at the top of the
borehole discharges the return mud from the annular space 19
between the walls of the borehole and the drillstring 2 into the
mud pit 13.
During operations, the mud pump 15 delivers mud 14 in a circuit in
the direction of the arrow 20 from the mud tank, downward through
the interior of the drillstring 2, up through the annulus 19 to the
drill head 12, through the return pipe 17 into the mud pit. The mud
pump is driven by motor 22 of constant output and accordingly
delivers the mud at a constant flow rate into the main pipe 16.
Connected to the main pipe 16 and discharging into the mud pit 13
is a branch pipe 23 that has a shut-off valve 24. The shut off
valve 24 is controlled by controller 25. In the preferred
embodiment, the controller is a computer or a processor. By
manipulating the shut-off valve 24, the branch pipe 23 may be
completely closed or completely opened to allow a portion of the
mud to bypass the mud flow to the borehole 5 as shown by the arrow
26. In the preferred embodiment, the shut-off valve 24 is designed
to allow adjustment of the maximum flow through the shut-off valve.
In the preferred embodiment, this is accomplished by a using a disc
valve in which two slots are moved relative to each other to change
the effective nozzle area. The controller 25 adjusts the relative
positions of the two slots to adjust the maximum flow deviation in
response to the measured downhole flow rate. Such disc valves are
known and are not described here.
In an alternate embodiment, the shut-off valve does not have an
adjustment for maximum flow rate; instead, downstream of the
shut-off valve, there is a throttle 27, by which the maximum amount
of volumetric flow change brought about by the branch pipe 23 is
controlled. The throttle is also controlled by the controller
25.
During uninterrupted drilling operations, the flow of mud in the
main pipe 16 is substantially constant. In order to transmit data
downhole, the shut-off valve 24 is actuated so as to open the
branch pipe 23. This reduces the flow in the drillstring 2. This
change is detected downhole by a suitable device on the drilling
tool 4. In the preferred embodiment, this is a turbine/generator
combination (not shown) driven by the flow of mud in the
drillstring. Those versed in the art would be familiar with such a
turbine/generator driven by the flow of mud. Reduction in the rate
of flow of the mud would cause a reduction in the rotor speed of
such a turbine and hence its output voltage. Conversely, when the
shut-off valve is opened, there is an increase in the rate of flow
of mud downhole and a corresponding increase in the output voltage
of the generator. Other devices, such as a flow rate measurement
device or a pressure detector could be used for detection of pulses
downhole.
The turbine/generator combination is the preferred downhole
detection device because the output of the generator is used to
drive other downhole devices. The downhole detector sends a signal
(not shown) back to the surface indicating what has been decoded.
This is accomplished by using a conventional Measurement While
Drilling (MWD) telemetry system. The information to be transmitted
uphole is relatively small since all that is essential for the
invention is an indication of the data rate at which the downhole
detector is decoding. A number of known methods could be used for
sending this signal to the surface. This includes an acoustic
signal carried by either the mud flowing uphole or by the
drillstring or an electromagnetic signal carried by the
drillstring. These methods would be familiar to those versed in the
art.
Depending on the manner of actuation and design of the shut-off
valve, a pulse-like pattern can be imposed on the volumetric flow.
This is illustrated in FIG. 2 by the curve 52 of the volumetric
flow rate at the surface. The steepness of the flanks 53 depends
upon the way and the speed at which the shut off valve is actuated.
In order to make the understanding of the invention easier, for the
remainder of the discussion it is assumed that the flanks 53 are
vertical, so that the curve 52 looks like an idealized square wave
superimposed on the steady volumetric rate of flow.
FIG. 3a shows a comparison between an idealized series of pulses as
generated at the surface and the signal received downhole. The
curve 71 here is the volumetric bleed-off produced by the opening
and closing of the bypass valve rather than the volumetric flow in
the main pipe. It has an amplitude given by 75. After a time 72,
called the "wake-up" time, the surface signal is a square wave with
a period denoted by 77 and an amplitude denoted by 75. Also shown
in FIG. 3a is the downhole signal 73 corresponding to the
transmitted surface signal 71. As can be seen, the square wave is
considerably smoothed out and somewhat attenuated. Nevertheless, a
periodicity associated with 75 is still detectable. Given proper
decoding, the transmitted signal can still be recovered. The method
for decoding such a signal would be familiar to those knowledgeable
in the art.
FIG. 3b is simply a reproduction of a portion of FIG. 3a. The
transmitted signal 91, characterized by an amplitude 93 and a
period of 95 is shown. FIG. 3c is similar to FIG. 3b with a
transmitted signal 101 having an amplitude 103 and period 105.
However, the period 105 of the signal is less than the period 95 of
the signal in FIG. 3b. As long as the downhole signal corresponding
to this surface signal can be properly decoded, it can be seen that
the signal in FIG. 3c has the capability of carrying more
information than the signal in FIG. 3b. Within a given time
interval, more bits (zeros and ones) can be accommodated. One of
the features of the present invention is the ability to vary the
time period of the signal.
FIG. 3d illustrates another variation of the transmitted signal. In
FIG. 3d, the transmitted signal 111 has the same period 115 as the
signal in FIG. 3b; however, its amplitude 113 is different. This is
accomplished by changing the maximum amount of the volumetric flow
possible in the branch pipe 23. FIG. 3e illustrates yet variation
of the transmitted signal. Here, both the amplitude 123 and the
period 125 of the pulse are different from the reference pulse in
FIG. 3b.
As would be familiar to those versed in the art, a data message can
be coded as a sequence of zeros and ones. The present invention can
be used to perform communication from the surface to the downhole
equipment by encoding the sequence of square wave pulses discussed
above with the sequence of zeros and ones describing the message to
be transmitted. This encoding is readily performed by modulating
the square wave pulse with the sequence of zeros and ones
describing the data. FIG. 4 illustrates the result of modulating a
square wave sequence. The top curve 151 illustrates an unmodulated
square wave sequence having a period 153. The data message denoted
by 155 corresponds to the binary sequence 10011. The result of
modulating the square wave sequence 151 by the modulating signal
155 is the curve 157. This can be used to change the flow rate and
control the downhole equipment for a variety of purposes, including
control signals for a directional drilling tool, signals for
switching operating modes of individual components of the
underground system.
The ability to vary both the amplitude and the period of the signal
is the basis for the adaptive nature of the present invention. The
changes in the period can also be encoded as part of the signal.
The first bit, which is used to start the data transmission, takes
on one of a discrete set of values. The initial pulse is made
sufficiently wide so that the detection device is always able to
determine the beginning of the command signal, i.e., able to wake
up. Corresponding to each of these values of the initial pulse is a
value of the data rate to follow. For example, a data rate of 8
seconds might correspond to an initial pulse of 20 seconds, a data
rate of 12 seconds would correspond to an initial pulse of 25
seconds while a data rate of 16 seconds would correspond to an
initial pulse of 30 seconds. These values are for illustrative
purposes only and in actual practice, many more values could be
used. In actual practice, the pulse width is maintained at the
shortest time period that is detectable by the downhole device. The
downhole tool sends a response signal back to the surface control
device indicating that a pulse has been detected downhole. If,
within a prespecified time interval after initiating a pulse
sequence, the surface control unit fails to receive a response
signal indicating detection of the pulse, the surface control unit
adjusts the parameters of the pulse to increase the likelihood of
detection. For example, the data period could be increased in steps
of, say, 2 seconds, until it is correctly detected and an
indication received at the surface. Alternatively, the amplitude of
the pulses is increased. This is done by changing the maximum flow
through the shut-off valve 24. As noted above, this is done by
adjusting a throttle in the branch pipe 23 or by using a valve,
such as a disc valve, as the shut-off valve. If, however, the
amplitude is already at the maximum possible value for the
apparatus, the period would be increased. Following this, the
encoded data is used to determine the flow rate of the mud.
Persons of ordinary skill in the art will appreciate that many
modifications may be made to the embodiments described herein
without departing from the spirit of the present invention.
Accordingly, the embodiments described herein are illustrative only
and are not intended to limit the scope of the present
invention.
* * * * *